JP 6-25484A discloses a rubber composition used for making a vibration-proof material, the rubber composition comprising an ethylene-α-olefin-non-conjugated diene copolymer rubber, which satisfies the following conditions (a) to (e):
(a) said copolymer rubber contains 60 to 90 parts by weight of an ethylene unit and 10 to 40 parts by weight of an α-olefin unit, wherein the total amount of both units is 100 parts by weight;
(b) said copolymer rubber has an iodine value of 3 to 40;
(c) an oil extended rubber composed of 100 parts by weight of said copolymer rubber and 70 parts by weight of an extender oil has a Mooney viscosity (ML1+4 121° C.) of 25 to 70;
(d) said oil extended rubber has a stress-relaxation rate of 0.19 or lower; and
(e) said copolymer rubber contains 0.5 to 50% by weight of xylene-insoluble matter at 100° C., wherein the amount of said copolymer rubber is 100% by weight.